The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Power amplifiers are used in many applications. For example, power amplifiers are used in output stages of transmitters of communication devices. Power amplifiers are also used in receivers, voltage regulators, driver circuits that drive motors, and so on. Power amplifiers are often included in integrated circuits. To save power consumed by the integrated circuits, power amplifiers are typically turned on and off as required. For example, in a transmitter, a power amplifier is turned on when the transmitter transmits data and is turned off when the transmitter does not transmit data. As the power amplifier is turned on and off, the local power dissipation in the area surrounding the power amplifier changes significantly. Over time, in a die that includes the power amplifier, points farther away from the power amplifier reach an average temperature. Locally, in an area proximate to the power amplifier, however, there is a thermal transient every time the power amplifier is turned on and off.
The gain of the power amplifier is sensitive to temperature variations. The gain typically decreases as temperature increases. The gain can therefore drift over time due to self-heating of the power amplifier. The gain variation due to self-heating of the power amplifier can cause problems. For example, in some systems, transmit power is set at the beginning of a transmission and is not adjusted during the transmission. The gain of the power amplifier and therefore the transmit power of the power amplifier may change due to self-heating of the power amplifier during the transmission. The gain change may cause errors in transmit signals transmitted by the transmitter. Small changes in the gain of the power amplifier translate into large error vector magnitude (EVM). It is therefore desirable to reduce the size of the gain change of the power amplifier due to thermal transients.